Piezoelectric voice range transducer



May 16, 1967 c. c. SIMS PIEZOELECTRIC VOICE RANGE TRANSDUCER Filed May 27, 1965 EXCITATION AND UTILIZATION MEANS INVENTOR cmuas a. $1 445 BY W ast-NT ATTORNEY United States atent O PIEZUELECTRIC VOICE RANGE TRANSDUCER Claude C. Sims, 1308 Heron Drive, Orlando, Fia. 82803 Filed May 27, 1965, Ser- No. 459,483 4 Claims. (Cl. 34t)--10) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to electroacoustical transducers in general and more particularly to an improved Voice range transducer or loudspeaker for producing high energy sound waves of very good quality in an aqueous medium intelligible to the naked ear over a very long range.

Heretofore voice range transducers have been available in the form of voice coils or modulated carriers which have their limitations such as very low frequency or a requirement of extra equipment at the listener. Other underwater loudspeakers have been produced which are too bulky, too heavy, of low fidelity, short range or other difiiculties.

The present invention overcomes the disadvantages of the prior art by providing a high efficient relatively light weight, long range underwater loudspeaker which can be heard by the naked ear without the use of extra equipment.

It is therefore an object of the present invention to provide an underwater loudspeaker which can be intelligibly heard over a long range.

Another object is to provide an underwater loudspeaker that is of light weight and compact in size.

Yet another object is to provide an underwater loudspeaker that is easily assembled and comparatively economical to manufacture and maintain.

Still another object is to provide a highly eificient voice range transducer.

Other objects and advantages of this invention will be readily apreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawing, in which:

FIG. 1 is a block diagram illustrating the cooperation between the transducer and the piezoelectric excitation means.

FIG. 2 is a cross sectional view of the device illustrating the relationship of the various parts of the transducer.

Referring now to the drawing there is shown by illustration a transducer or underwater loudspeaker having an elongated cylindrical tubular housing 11 formed of aluminum, metal, fiber glass, plastic, or any other suitable material having the proper characteristics adapted for effecting mechanical impedance transformation between the housing and the ambient fluid. An electrostrictive energy converter 12 is assembled within the housing coaxial therewith between two diaphragms 13 and 14 by use of a compression bolt 15 and insulated therefrom by any suitable insulation 20. Diaphragms 13 and 14 are identical with the exception that diaphragm 13 has a threaded hole 16 therein which receives the compression bolt 15 that passes through an aperture 17 in diaphragm 14. The compression bolt is provided with suitable O-rings 18 which provide a seal between the diaphragm 14 and the bolt 15 to prevent leakage of fluid into the energy converter compartment of the device. The diaphragms are provided with O-rings 19 about the circumference thereof to provide a seal between each of the diaphragms and the inner wall of the housing.

The electrostrictive energy converter includes a stack 3,323,58l Patented May 16, 1967 of a plurality of piezoelectric elements 21 of ferroelectric, polarized barium titanate ceramic, lead zirconate or any other ferroelectric or electrostrictive ceramic or the like. Each element is made as a ring and is provided with a thin electrode 22 on each face thereof in the axial direction. Each element is then stacked coaxially within the housing in such a manner that adjacent electrodes contact each other. The piezoelectric elements are then connected electrically in parallel by any suitable means such as insulated wire and secured between the diaphragms 13 and 14 under compression by the compression bolt 15 which passes through the peizoelectric rings along the axis thereof. It is to be understood that the piezoelectric elements may be connected in series electrically if operational requirements warrant such a connection and that the elements may be so insulated to enable such a connection.

A suitable transformer 23 is secured to the inner surface of the housing in the area confined by the two diaphragms and centered on a plane through the median of the housing. A water-proof connector 24 is secured in an aperture through the housing through which electrical leads 25 pass to electrically connect the primary of the transformer with an excitation and utilization means 28 remote from the transducer. The transformer 23 has a low impedance primary winding adapted to match a 16 ohm power source input. The secondary winding of the transformer is electrically connected with the piezoelectric elements 21 which are connected in parallel electrically.

A sound deflection bafiie may be secured to each end of the housing to deflect the sound waves, however this is not necessary for carrying out the invention and is not shown for that reason.

In assembling the device, the transformer, and water proof electrical connector is secured to the cavity or housing and the electrical lead lines from the source to the transformer are connected into place. The diaphragm 13 which receives the threaded end of the compression bolt is positioned into the housing. The piezoelectric elements are assembled in the housing coaxial therewith, connected electrically in parallel, and connected electrically to the secondary winding of the transformer. The diaphragm having the axial aperture 17 therein through which the compression bolt 15 is passed is positioned into place over the piezoelectric stack. The compression bolt is inserted through the aperture in diaphragm 14 and screw threaded into the threaded hole in diaphragm 13 or the bolt is threaded into the diaphragm l3 and diaphragm 14 is placed over the bolt. The compression bolt is drawn taut by a suitable nut threaded onto the bolt to place the piezoelectric stack under slight compression. The bafiles, if desired, may then be secured to the ends of each cavity. Each of the diaphragms and the compression bolt are provided with appropriate 0- ring seals to prevent fluid leakage into the area of the transformer and the piezoelectric stack.

In operation, the electrical leads from the water proof connector are connected to an appropriate excitation and utilization means such as a conventional 16 ohm source. The loudspeaker is submerged completely in water with the axis of the cavity vertical where it projects an omnidirectional pattern of wave energy in the acoustical range of frequencies especially in the voice range.

When broadcasting, the piezoelectric stack is excited by a transmitter through the transformer which results in an expansion and contraction of the piezoelectric stack in accordance with the intelligence characteristics of the electrical voltage applied to the piezoelectric elements. Because the piezoelectric elements are stacked along a common operational axis, the relative movement of each element is additive and becomes the sum of the expansions and contractions of all the elements combined. Thus, water opposite the ends of the piezoelectric elements move axially according to the movement of the piezoelectric elements. As a result, the diaphragms react on the fluid in the cavities at the ends of the housing which in turn results in compression and decompression of the ambient water. The cavities radiate into the water wherein the sound waves produced are omnidirectional.

An underwater loudspeaker made in accordance to the present invention may be made in different sizes, however, it has been determined that for best results, the housing should have a diameter of about eight inches,

7 with a length of about eleven inches, and a wall thickness /2) to withstand the pressure at which the transducer is to be operated. The diaphragms each have a thickness of about one inch and are positioned with their outer face surface about three inches from the end of the housing. Thus, the piezoelectric elements are each about one half inch in height, and about 2% inches in circumference. Obviously the dimensions and materials may be changed, however for best voice range results the dimensions should be in the range of those described.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An underwater loudspeaker operable in the voice range which comprises:

an open ended cylindrical tubular housing,

first and second diaphragms secured within said housing in a fluid tight relationship with respect to the inner wall surface of said housing equidistant from and parallel with a plane through the center of said housing perpendicular to the axis of said housing,

a piezoelectric energy converter means secured within said housing between said first and second diaphragms under slight compression,

means passing through said piezoelectric energy converter means coaxial therewith and mechanically secured to said first and second diaphragms for slightly compressing said piezoelectric energy converter means,

a transformer having a primary and secondary winding mounted within said housing in the area between said diaphragms,

said secondary winding of said transformer electrically coupled to said piezoelectric energy converter to supply electrical power thereto, and

means connected with said primary winding of said transformer for conducting electrical energy thereto from a source externally of said housing.

2. An underwater loudspeaker operable in the voice range which comprises:

an open ended cylindrical tubular housing,

first and second diaphragms secured within said housing in a fluid tight relationship with respect to the inner wall surface of said housing equi-distant from and parallel with a plane through the center of said housing perpendicular to the axis thereof,

a piezoelectric energy converter means including a plurality of rings of piezoelectric material secured within said housing coaxial therewith between said first and second diaphragms under a slight compression,

means passing through said piezoelectric energy converter means coaxial therewith and mechanically secured to said first and second diaphragms for slightly compressing said piezoelectric energy converter means,

a transformer mounted within said housing in the area between said diaphragms,

said transformer electrically coupled to said piezoelectric energy converter to supply electrical power thereto, and

means connected with said transformer for conducting electrical energy thereto from a source externally of said housing.

3. An underwater loudspeaker operable in the voice range which comprises:

an open ended cylindrical tubular housing having a wall thickness sufficient to withstand ambient pressures,

first and second diaphragms secured within said housing equi-distant from and parallel with a plane through the mid-point of said housing perpendicular to the axis thereof,

a piezoelectric energy converter means,

said piezoelectric energy converter means including a plurality of cylindrical rings secured within said housing coaxial therewith between said first and second diaphragms under slight compression,

means passing through said piezoelectric energy converter means coaxial therewith and mechanically secured to said first and second diaphragms for slight- 'ly compressing said piezoelectric energy converter means,

a transformer having a primary and a secondary winding mounted within said housing in the area confined by said diaphragms,

said secondary winding of said transformer electrically coupled to said piezoelectric energy converter to supply electrical power thereto, and

means connected with said primary winding of said transformer for conducting electrical energy thereto from a source externally of said housing.

4. An underwater voice range transducer as claimed in claim 3 wherein:

said piezoelectric rings are of the same dimension, and

adjacent faces are provided with electrodes that are connected electrically with said secondary winding of said transformer.

References Cited by the Examiner UNITED STATES PATENTS 2,891,233 6/1959 Crandell 340-10 X 3,113,288 12/1963 Snavely 3401O 3,177,382 4/1965 Green 340-10 X RODNEY D. BENNETT, Primary Examiner.

J. P. MORRIS, Assistant Examiner, 

1. AN UNDERWATER LOUDSPEAKER OPERABLE IN THE VOICE RANGE WHICH COMPRISES: AN OPEN ENDED CYLINDRICAL TUBULAR HOUSING, FIRST AND SECOND DIAPHRAGMS SECURED WITHIN SAID HOUSING IN A FLUID TIGHT RELATIONSHIP WITH RESPECT TO THE INNER WALL SURFACE OF SAID HOUSING EQUI-DISTANT FROM AND PARALLEL WITH A PLANE THROUGH THE CENTER OF SAID HOUSING PERPENDICULAR TO THE AXIS OF SAID HOUSING, A PIEZOELECTRIC ENERGY CONVERTER MEANS SECURED WITHIN SAID HOUSING BETWEEN SAID FIRST AND SECOND DIAPHRAGMS UNDER SLIGHT COMPRESSION, MEANS PASSING THROUGH SAID PIEZOELECTRIC ENERGY CONVERTER MEANS COAXIAL THEREWITH AND MECHANICALLY SECURED TO SAID FIRST AND SECOND DIAPHRAGMS FOR SLIGHTLY COMPRESSING SAID PIEZOELECTRIC ENERGY CONVERTER MEANS, A TRANSFORMER HAVING A PRIMARY AND SECONDARY WINDING MOUNTED WITHIN SAID HOUSING IN THE AREA BETWEEN SAID DIAPHRAGMS, SAID SECONDARY WINDING OF SAID TRANSFORMER ELECTRICALLY COUPLED TO SAID PIEZOELECTRIC ENERGY CONVERTER TO SUPPLY ELECTRICAL POWER THERETO, AND MEANS CONNECTED WITH SAID PRIMARY WINDING OF SAID TRANSFORMER FOR CONDUCTING ELECTRICAL ENERGY THERETO FROM A SOURCE EXTERNALLY OF SAID HOUSING. 